1. Field of the Invention
The invention relates generally to electronic switches, and, more particularly, to capacitive micro-electro-mechanical system (MEMS) switches.
2. Description of Related Art
Capacitive MEMS may be used in RF switches, phase arrays, phase scanning, compensating circuits, filters, beam matrices, channel switching, and the like. Generally, capacitive switches typically operate by suspending a flexible, conductive membrane over a dielectric layer, which is coupled to at least one electrode. In a normal xe2x80x9cOFFxe2x80x9d state, that is, when no DC voltage is applied to the electrode, the conductive membrane is suspended without touching the dielectric layer. In an xe2x80x9cONxe2x80x9d state, that is, when a voltage is applied to the electrode, however, the conductive membrane is xe2x80x9cpulled downxe2x80x9d to the dielectric layer, which produces an increased capacitance allowing high-frequency signals to be transmitted between the conductive membrane and the electrode.
Capacitive switches, however, experience a dielectric charging when the flexible, conductive membrane has a high voltage on it, and comes in contact with the dielectric layer. While this dielectric layer gives the switch a desirable on-capacitance (due to its high relative dielectric constant), this layer also experiences a dielectric-charging phenomenon, which limits the life expectancy of the switch. For example, with 50 volts across a 0.2 micron thick dielectric layer, an electric field of 2.5 MV/cm is present across the dielectric layer. It has been shown that electric fields on the order of 1-5 MV/cm cause quantum-mechanical tunneling of charges into the dielectric. These charges become trapped within the dielectric layer due to its insulating properties. Over time and actuations, these charges build up a voltage that screens (subtracts) from the applied field, ultimately causing the switch to stick in the down position, or not actuate when desired. At this point, the switch has failed. Proper operation of the switch cannot resume until these charges have slowly bled off, which can take from days to weeks, depending on the purity and conductivity of the dielectric layer.
Therefore, there is a need for a capacitive MEMS switch that prevents the storing of charges in the dielectric layer, thereby increasing reliability and the life expectancy of the switch.
The present invention provides a proximity micro-electro-mechanical system (MEMS) device that utilizes a gaseous capacitive gap. The MEMS comprises a second electrode suspended above at least one first electrode. At least one insulating support prevents at least a portion of the second electrode from contacting at least a portion of the first electrode, maintaining the gaseous capacitive gap. When voltage is applied to the electrode, the flexible membrane is drawn towards the electrode and charges the gaseous capacitive gap.